Leaf Spot and Melting Out

News Article

Turf samples showing symptoms of leaf spot and melting out have been arriving in the Plant Disease Clinic. Leaf spots on grass blades are initially reddish brown to dark brown. As they enlarge, they take on an oblong shape and develop a gray to light tan center with a dark border. Heavily infected blades may turn yellow, wither, and die. The activity of the fungus can also move to the crown of the plant and cause collapse and death of plants. This is referred to as melting out, because the overall appearance is a severe thinning of the turf. There are a number of cultural management practices that aid in controlling turfgrass diseases.

  • Avoid frequent, short irrigations, especially in the evening. Water should be applied to wet the soil deeply but as infrequently as possible without causing stress.
  • Limit thatch to one half-inch or less. (Thatch is the accumulated layer of living and dead plant parts that build up between the soil surface and the green of grass blades.)
  • Provide good surface and subsurface drainage; fill in low spots where water may stand.
  • Grow disease resistant grasses in blends or mixtures; in shaded areas, grow shade tolerant cultivars.
  • Apply fertilizers as needed to encourage moderate plant growth, but avoid rates that cause excessive growth.
  • Mow frequently at recommended height (remove no more than one-third of the leaf height at one cutting). Keep mower blades sharp.
  • ;Increase light penetration and air movement to the turfgrass area and speed drying of the grass by selective pruning of trees, shrubs, and hedges.
  • Fungicides can also be used, but a full-season spray program is needed. Spraying every 10-14 days all season is impractical in most situations. Therefore, the cultural controls are generally the most practical.

This article originally appeared in the June 12, 1998 issue, p. 77.

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